The present invention relates to a method and apparatus for controlling track jump, and more particularly, to a method and apparatus for controlling track jump in a data reproduction apparatus that reads digital data from a disc type recording medium and transfers the data to a computer.
A compact disc (CD) is mainly used as a digital audio recording medium, but it can also be used as a read only memory (CD-ROM) for storing various types of digital data read by computers.
FIG. 1 is a schematic block diagram showing a conventional disk reproduction apparatus. A disc 1 has a spiral recording track formed on at least one of its surfaces. Digital data, which is in a predetermined format, is recorded along the recording track. The disc reproduction apparatus includes a pickup 3 to read the data recorded on the recording track. The disc reproduction apparatus further includes a servo mechanism for controlling the position of the pickup 3 relative to the disc 1 so that the pickup 3 tracks the recording track properly.
The pickup 3 is arranged opposite the recording track of the disc 1. An actuator 4, which is operated in accordance with a drive signal TD, moves the pickup 3 in the radial direction of the disc 1. The pickup 3 includes laser beam sources and sensors. Referring to FIG. 2, the pickup 3 generates a main reading beam P and a pair of auxiliary reading beams T1, T2 which are radiated toward the recording track. The pickup 3 has a main beam receiving portion and an auxiliary beam receiving portion. The main reading beam P is received by the main beam receiving portion to detect pits on the recording track surface. The auxiliary reading beams T1, T2 are received by the auxiliary beam receiving portion to detect when the pickup 3 moves away from the recording track. The reading beams P, T1, T2 radiated against the pits of the disc 1 are reflected toward the beam receiving portions as weak lights. The reading beams D, T1, T2 radiated against portions other than the pits of the disc 1 are reflected toward the beam receiving portions as strong lights. When the beam receiving portion associated with each of the reading beams P, T1, and T2 receives the corresponding reflection beam, the receiving portion generates a voltage having a value which corresponds to the intensity of the reflected light. The actuator 4 supports the pickup 3 and performs track jump to move the pickup 3 radially along the disc 1 in response to the drive signal TD.
The pickup 3 sends a voltage signal, the value of which corresponds to the main reading beam P, to a signal processor 5. The signal processor 5 performs a waveform shaping process and a digitizing process on the voltage signal to generate an EFM signal. The EFM signal repetitively goes back and forth between a low level and a high level in accordance with the existence of pits.
The signal processor 5 generates a tracking error signal TE from the difference between the voltage values of the auxiliary reading beams T1, T2 and an off track signal OT from a low frequency component of the EFM signal. The waveform of the tracking error signal TE is a sine wave, the polarity of which is inverted each time the pickup 3 moves across the recording track. The tracking error signal TE is digitized to generate a track jump signal TJ.
The voltage value corresponding to the auxiliary reading beam T1 is substantially the same as the voltage value corresponding to the auxiliary reading beam T2 when the pickup 3 is accurately tracking the recording track (i.e., when the pickup 3 is at the proper position). Under these conditions, the tracking error signal TE is at a null level. When the pickup 3 is not accurately tracking the recording track (i.e., when the pickup 3 is not at the proper position), for example, when the position of the pickup 3 is offset inward from the recording track, the voltage value corresponding to the auxiliary reading beam T1 becomes smaller than the voltage value corresponding to the auxiliary reading beam T2 and causes the tracking error signal TE to take a negative value. On the other hand, if the position of the pickup 3 is offset outward from the recording track, the voltage value corresponding to the auxiliary reading beam T2 becomes smaller than the voltage value corresponding to the auxiliary reading beam T1 and causes the tracking error signal TE to take a positive value. When the pickup 3 is completely separated from the recording track, the voltage values of the auxiliary reading beams T1, T2 become equal to each other and cause the tracking error signal TE to become null. The track jump signal TJ is generated from the tracking error signal TE using the null level as a threshold value. Further, the track jump signal TJ goes high or low when the center of the pickup 3 is located at the center of the recording track.
when the pickup 3 is properly tracking the recording track of the disc 1, the signal processor 5 continuously outputs the EFM signal. Thus, the EFM signal has a predetermined amplitude and does not include a low frequency component. Accordingly, the off track signal OT is maintained at a low level when the pickup 3 is properly tracking the recording track. The off track signal OT rises or falls when the center of the pickup 3 is located near an edge of a pit.
As shown in FIG. 1, the signal processor 5 sends the EFM signal, the tracking error signal TE, and the off track signal OT to the servo controller 6. The servo controller 6 generates a spindle motor drive signal SD and the actuator drive signal TD based on the tracking error signal TE and the off track signal OT. The spindle motor drive signal SD controls the spindle motor 2 so that the frequency of the EFM signal is maintained at a predetermined value. The actuator drive signal TD controls the actuator 4 so that the tracking error signal TE has a null level and the off track signal OT is maintained at a low level. The spindle motor drive signal SD and the actuator drive signal TD servo control the spindle motor and tracking.
FIGS. 3(a) and 3(b) are charts showing the waveforms of the signals detected when the pickup 3 moves across the lines of the recording track on the disc 1 (when a so-called track jump is performed). The horizontal axis represents time. FIGS. 3(a) and 3(b) show a state in which the pickup 3 gradually decelerates.
As described above, the track jump signal TJ rises or falls when the center of the pickup 3 is located at the center of the recording track. The off track signal OT rises or falls when the center of the pickup 3 is located near the edges of the pits. Accordingly, the phase difference between the off track signal OT and the tracking error signal TE is normally +90xc2x0. The tracking error signal TE or the off track signal OT are counted to detect the number of recording tracks the pickup 3 traverses. The moving direction of the pickup 3 is detected by the difference between the phase of the tracking error signal TE and the phase of the off track signal OT. The movement of the pickup 3 is controlled based on the two detection results.
The moving speed of the pickup 3 must be detected to perform the track jump. In other words, the pickup 3 is moved to the desired position by monitoring the moving speed of the pickup 3 and accelerating and decelerating the pickup 3 at optimal timings to decrease the moving time of the pickup 3. During a single cycle of the track jump signal TJ or the off track signal OT, a clock signal CLK is counted to measure the time of the cycle and detect the moving speed. The clock signal CLK, which is sent to the servo controller 6, has a cycle sufficiently advanced from the track jump signal TJ and the off track signal OT.
However, only the average speed during one cycle is obtained in the above speed measuring method. The resolution of the measured speed may then be insufficient and the measured speed may be inaccurate. Accordingly, the pickup 3 may not be able to stop precisely at the predetermined position, causing sliding to occur. In addition, if excessive force is applied to stop the movement of the pickup 3, the pickup 3 may stop before reaching the target position or may move in the reverse direction.
Accordingly, it is an object of the present invention to provide a track jump control method and control circuit for accurately controlling the moving speed of the pickup.
To achieve the above object, the present invention provides a method for controlling track jump on a disc by a pickup. The method includes the steps of generating a pulse signal corresponding to changing points of a track jump signal and an off track signal, and generating a signal for controlling the moving speed of the pickup in accordance with the pulse signal.
Another aspect of the present invention provides a method for controlling track jump on a disc by a pickup. The method includes the steps of generating a track jump signal having a first changing point when the pickup is located above a track and a second changing point when the pickup is located between adjacent tracks, and generating an off track signal indicating a first state when the pickup is located above a track and a second state when the pickup is located apart from the track. The off track signal is changed from the first state to the second state at a third changing point and changed from the second state to the first state at a fourth changing point. The method also includes the steps of dividing a cycle of the track jump signal and the off track signal into four periods at the first to fourth changing points of the track jump signal and the off track signal, and measuring the length of the divided four periods, and controlling the moving speed of the pickup in accordance with the lengths of the divided four periods.
A further aspect of the present invention provides a method for controlling track jump on a disc by a pickup. The method includes generating a track jump signal having a first changing point when the pickup is located above a track and a second changing point when the pickup is located between adjacent tracks, and generating an off track signal indicating a first state when the pickup is located above a track and a second state when the pickup is located apart from the track. The off track signal is changed from the first state to the second state at a third changing point and changed from the second state to the first state at a fourth changing point. The method further includes the steps of detecting one of the first changing point and the second changing point of the track jump signal corresponding to one of a target track to where the pickup jumps and a track located a predetermined number of tracks before the target track, decelerating the pickup when one of the first changing point and the second changing point is detected, measuring the time between one of the first changing point and the second changing point and one of the third changing point and the fourth changing point of the subsequently generated off track signal, and adjusting the deceleration of the pickup in accordance with the measured time.
In a further aspect, the present invention provides a circuit for controlling track jump on a disc by a pickup. The circuit includes a first circuit for generating a pulse signal corresponding to changing points of a track jump signal and an off track signal, and a second circuit for generating a signal for controlling the moving speed of the pickup in accordance with the pulse signal.
In a further aspect, the present invention provides a circuit for controlling track jump on a disc by a pickup. The circuit includes a measuring circuit for receiving a track jump signal, which has a first changing point and a second changing point, and an off track signal, which has a third changing point and a fourth changing point, and measuring a length between one of the first changing point and the second changing point of the track jump signal and one of the third changing point and the fourth changing point of the off track signal. The first changing point occurs when the pickup is located above a track, the second changing point occurs when the pickup is located between adjacent tracks, the third changing point occurs when the off track signal changes from a first state to a seconded state, and the fourth changing point occurs when the off track signal changes from the second state to the first state. A control circuit is connected to the measuring circuit to generate a drive signal corresponding to the measured result of the measuring circuit.
In a further aspect, the present invention provides a circuit for controlling track jump on a disc by a pickup. The circuit includes a measuring circuit for receiving a track jump signal, which has a first changing point and a second changing point, and an off track signal, which has a third changing point and a fourth changing point, and measuring the length between one of the first changing point and the second changing point of the track jump signal and one of the third changing point and the fourth changing point of the off track signal. The first changing point occurs when the pickup is located above a track, the second changing point occurs when the pickup is located between adjacent tracks, the third changing point occurs when the off track signal changes from a first state to a second state, and the fourth changing point occurs when the off track signal changes from the second state to the first state. A track counter detects one of the first changing point and the second changing point of the track jump signal corresponding to one of a target track to where the pickup jumps and a track located a predetermined number of tracks before the target tracks. A control circuit is connected to the measuring circuit and the track counter for generating a drive signal when one of the first changing point and the second changing point is detected by the track counter. The control circuit controls deceleration of the pickup by adjusting the drive signal in accordance with the time measured by the measuring circuit.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.